Anti-reflective imaging layer for multiple patterning process

ABSTRACT

Novel methods of double patterning a photosensitive resin composition are provided. The methods involve applying the photosensitive composition to a substrate and thermally crosslinking the composition. The crosslinked layer can be used to provide reflection control. Upon exposure to light, the crosslinked polymer (or oligomer or monomer) in the compositions will decrosslink, rendering the light-exposed portions soluble in typical photoresist developing solutions (e.g., alkaline developers). Advantageously, the crosslinked portions of the composition remain insoluble in the solvent used to form the photosensitive composition. As a result, the coating, lithographic, and or developing steps can be repeated multiple times in varying order, depending upon the particular process, without destroying earlier-formed patterns.

RELATED APPLICATIONS

This application claims the priority benefit of a provisionalapplication entitled ANTI-REFLECTIVE IMAGING LAYER FOR MULTIPLEPATTERNING PROCESS, Ser. No. 60/822,823, filed Aug. 18, 2006,incorporated by reference herein

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is broadly concerned with novel, double patterningmethods that utilize a thermally crosslinkable, photosensitivecomposition.

2. Description of the Prior Art

Trends toward improving the photolithography process include the use ofhigh numerical aperture (NA) tools and/or immersion fluids. Usingimaging tools with high NA capabilities (>1.0) by themselves or incombination with immersion provides a method to achieve higherresolution of patterns with smaller critical dimension and higherdensity. These advances are possible because of the larger amount oflight that can be transferred to the imaging layer. However, theseoptions are quite costly and require new tool sets.

Multi-patterning techniques, have been used to attempt to achievehigh-density lithography. However, these are lacking in that photoresistpatterns are destroyed by repeated photoresist applications.

There is a need for improved methods to allow higher-density patterningutilizing presently available equipment.

SUMMARY OF THE INVENTION

The present invention overcomes these problems by broadly providing amethod of forming a microelectronic structure. The method comprisesapplying a photosensitive composition to the surface of a substrate toform an imaging layer adjacent the substrate surface. The components(e.g., polymers, oligomers, compounds) in the imaging layer are thencrosslinked, and the layer is exposed to light to yield light-exposedportions in said layer that have been chemically modified as a result ofthis light exposure. The imaging layer is contacted with a developer,preferably an aqueous alkaline developer, so as to remove thelight-exposed portions from the substrate and form a patterned imaginglayer.

A second photosensitive composition is then added to form a secondimaging layer on the patterned imaging layer. This is accomplishedwithout first heating the patterned imaging layer, which would have beenessential in prior art processes. That second imaging layer can then bepatterned and developed, and this coating/patterning/developing processcan be repeated multiple times if desired. After the process has beenrepeated sufficiently to form the desired pattern in the imaging layer,that pattern can be transferred to the substrate.

In another embodiment, the crosslinked imaging layer is exposed to lightto yield the light-exposed portions in said layer. Then, the layer issubjected to one or more additional light-exposure steps, with each stepyielding more light-exposed portions in the imaging layer. After thedesired exposures have occurred, a single development step can becarried out to remove all light-exposed portions, yielding a patternedimaging layer that can ultimately be transferred to the substrate.Alternatively, a development step can be carried out after each lightexposure step in order to remove the light-exposed portions prior to thenext light exposure step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing illustrating a process according to theinvention

FIG. 2 is a schematic drawing illustrating a second embodiment of theinventive process; and

FIG. 3 is a schematic drawing illustrating a third embodiment of theinventive process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The Inventive Method

FIG. 1 illustrates one embodiment of the inventive process. A substrate10 having an upper surface 12 is provided. Any conventionalmicroelectronic substrate can be utilized, including substratescomprising one or more of the following: silicon, aluminum, tungsten,tungsten silicide, gallium arsenide, germanium, tantalum, tantalumnitride, SiGe, and mixtures of the foregoing.

As shown in step (a), a thermally crosslinkable and photochemicallydecrosslinkable composition is applied to the surface 12 to form animaging layer 14 having an upper surface 16. The composition can beapplied by any known application method, with one preferred method beingspin-coating the composition at speeds of from about 750 rpm to about3,500 rpm (preferably from about 1,000 rpm to about 2,500 rpm) for atime period of from about 10 seconds to about 120 seconds (preferablyfrom about 20 seconds to about 60 seconds).

The layer 14 is then baked so as to induce thermal crosslinking of thelayer 14. Preferred baking conditions involve temperatures of at leastabout 100° C., preferably from about 100° C. to about 250° C., and morepreferably from about 120° C. to about 200° C., and for time periods offrom about 10 seconds to about 90 seconds. The thickness of thecrosslinked imaging layer 14 will typically be from about 10 nm to about150 nm, and preferably from about 30 nm to about 80 nm.

The crosslinked layer 14 will be sufficiently crosslinked that it willbe substantially insoluble in typical photoresist solvents (includingthe solvent that was present in the photosensitive composition used toform layer 14). Thus, when subjected to a stripping test, thecrosslinked layers 14 will have a percent stripping of less than about5%, preferably less than about 1%, and even more preferably about 0%.The stripping test involves first determining the thickness (by takingthe average of measurements at five different locations) of the curedlayer. This is the initial average film thickness. Next, a solvent(e.g., ethyl lactate, PGME, PGMEA) is puddled onto the cured film forabout 10 seconds, followed by spin drying at about 2,000-3,500 rpm forabout 20-30 seconds to remove the solvent. The thickness is measuredagain at five different points on the wafer using ellipsometry, and theaverage of these measurements is determined. This is the average finalfilm thickness.

The amount of stripping is the difference between the initial and finalaverage film thicknesses. The percent stripping is:

${\%\mspace{14mu}{stripping}} = {( \frac{{amount}\mspace{14mu}{of}\mspace{14mu}{stripping}}{{initial}\mspace{14mu}{average}\mspace{14mu}{film}\mspace{14mu}{thickness}} ) \times 100.}$

In the embodiment of FIG. 1, the best use of layer 14 would typically besimply as an imaging layer. In these instances, the k value (imaginarycomponent of the complex index of refraction) is preferably from about 0to about 0.5.

At step (b), a mask 18 is positioned above the surface 16 of imaginglayer 14, and light 20 is directed at the mask 18. The mask 18 has openareas 22 designed to permit light to pass by the mask 18 and contactsurface 16 of imaging layer 14. The remaining solid portions 24 of mask18 are designed to prevent light from contacting surface 16 of imaginglayer 14 in certain areas. Those skilled in the art will readilyunderstand that the arrangement of open areas 22 and solid portions 24is designed based upon the desired pattern to be formed in imaging layer14 and ultimately in the substrate surface 12. The present inventiveprocess can be used with UV light of most wavelengths, but wavelengthsof 157 nm, 193 nm, 248 nm, and 365 nm are most preferred.

Upon being exposed to light, the portions 26 of the imaging layer 14that are exposed to light undergo a photochemical reaction so that thelayer 14 is photochemically decrosslinked. More specifically, an acid isgenerated from the PAG upon exposure to light, and this acid“decrosslinks” the polymer, oligomer, or compound in the layer. That is,the acid catalyzes the breaking of the bond that was formed between thepolymer, oligomer, or compound and the crosslinker upon thermalcrosslinking. After light exposure the imaging layer 14 is preferablysubjected to a post-exposure bake (as used herein, post-exposure bakesare carried out at a temperature of less than about 150° C., preferablyless than about 140° C., and more preferably from about 90° C. to about140° C. for a time period of from about 30 seconds to about 90 seconds).

Advantageously, the light-exposed portion 26, which was made developersoluble with the above steps, is contacted with a developer as shown instep (c). The developer removes the portions 26 of imaging layer 14 toleave behind openings 28. Openings 28 can be holes, trenches, spaces,etc., and will ultimately be transferred to the substrate 10. “Developersoluble” as used herein means the portions 26 that have been exposed tolight can be substantially removed with conventional aqueous developerssuch as tetramethyl ammonium hydroxide and KOH developers. At leastabout 95%, preferably at least about 99%, and even more preferably 100%of the portions will be removed by a base developer such as tetramethylammonium hydroxide and/or KOH developers.

The inventive process is particular advantageous in that it is adouble-patterning process. That is, the stack 30 that has been coated,subjected to lithography, and developed, can now be coated, subjected tolithography, and developed again to create further patterns, Referringto step (d), a thermally crosslinkable and photochemicallydecrosslinkable composition is applied to form a second imaging layer 32having an upper surface 34. Because the imaging layer 14 wascrosslinked, this second coating step is possible while stillmaintaining the previously-formed pattern intact. Furthermore, thislayer remains intact without requiring an additional heating (hardening)step to be carried out on the imaging layer 14. So, in this embodimentand in all embodiments of this application, the only heating steps occurduring thermal crosslinking and during any post-exposure bakes.

The composition application would be similar to that described abovewith respect to step (a). Furthermore, one would typically use the samethermally crosslinkable and photochemically decrosslinkable compositionused in the earlier step (a), but this is not required, and differentcompositions (e.g., a conventional photoresist for the secondphotosensitive composition) could be used if desired. The same bakingconditions would be followed as described in step (a), and the thickness“T” of the second imaging layer 32 on top of the highest remainingportion of imaging layer 14 would also be the same as described abovewith step (a).

In step (e), a mask 36 having the desired pattern formed therein ispositioned over surface 34 of second imaging layer 32, and lightexposure is repeated as described in step (b) above. Exposed portions 38are formed in second imaging layer 32, and the stack 40 is preferablysubjected to a post-exposure bake followed by contact with a developer(step (f)). This results in the removal of exposed portions 38 to leavebehind openings 42. Again, these openings 42 can be holes, trenches, orspaces. The raised portions 44 remaining on substrate surface 12 aretypically referred to as lines or raised features. This pattern ofholes, trenches, spaces, lines, and raised features will ultimately betransferred to the substrate 10.

The above coating, baking, light exposure, optional post-exposurebaking, and developing steps can be repeated as many more times asdesired and as is feasible for the particular pattern 46 to be formed insubstrate surface 12. The stack 48, which comprises substrate 10 andpattern 46 on substrate surface 12, is then subjected to an etchingprocess (e.g., plasma etch), whereby the pattern 46 is transferred tothe substrate 10, so that substrate 10 now includes the openings 42 andportions 44 formed therein. It will be appreciated that it is notnecessary to perform any etching steps prior to this point in theprocess. That is, steps (a)-(f) are carried out without any etchingoccurring. Half pitch dimensions of less than about 50 nm can beachieved with this method. The patterned substrate is then subjected tofurther fabrication steps (e.g., metallization).

FIG. 2 illustrates a second embodiment of the inventive process. Likenumbering is used for all embodiments to designate similar materials.The same process conditions (e.g., spin speeds, temperatures, timeperiods, wavelengths) as well as compositions, substrates, developers,and masks used as in FIG. 1 would be used in this embodiment.

In the embodiment of FIG. 2, a photoresist 45 having an upper surface 47is applied (e.g., via spin-coating) to the upper surface 16 of imaginglayer 12 after thermal crosslinking of imaging layer 12. During exposurestep (b), the light also chemically alters portion 27 of resist 45 tomake it more soluble in typical developers. After this exposure step (b)(and the optional post-exposure bake), the stack is not developed but isinstead immediately subjected to a second exposure step (c), whereanother mask 36 is utilized to create the second pattern in imaginglayer 26 and photoresist 45. This could be followed with more exposuresteps with other masks, if desired. Once the desired number of exposuresteps has been carried out, the imaging layer 14 and photoresist 45 aredeveloped (step (d)) to yield patterned layer 46. Conventional etching,metallization, etc., can then be carried out to complete the devicemanufacture.

In the embodiment of FIG. 3, a photoresist 45 is also utilized as wasthe case in FIG. 2. After exposure step (b), the stack is developed(step (c)) similar to the embodiment of FIG. 1. However, rather thanbeing subjected to a second coating step as was done in the embodimentof FIG. 1, imaging layer 14 and the photoresist 45 are subjected to asecond exposure step (d) with a second mask 36 to expose other portionsof layer 14 and resist 45 to light. After this exposure, the imaginglayer 14 and resist 45 are subjected to a second developing step (e) tofurther pattern the layers. This exposure-develop sequence can berepeated as many times as desired, after which the stack 48 is etched totransfer the pattern to the substrate 10, followed by subsequentprocessing such as metallization.

In the embodiments of FIGS. 2 and 3, it will again be appreciated thatit is not necessary to perform any etching steps prior to this point inthe process. That is, steps (a)-(d) of FIG. 2 and steps (a)-(e) of FIG.3 are carried out without any etching occurring. Furthermore, theprocess can be repeated with multiple photoresist layers (of the same ordifferent chemical composition) as desired for the particular process.

In the embodiments of FIGS. 2 and 3, the layer 14 would typically befunctioning as a bottom anti-reflective coating. In these instances, thecrosslinked layers will be formulated to provide superior lightabsorbance. The n value of the crosslinked layer 14 would be at leastabout 1.3, and preferably from about 1.4 to about 2.0, while the k valuewill be least about 0.1, and preferably from about 0.2 to about 0.5, atthe wavelength of use (e.g., 157 nm, 193 nm, 248 nm, 365 nm). The OD ofthe cured layers will be at least about 5/μm, preferably from about5-15/μm, and even more preferably from about 10-15 μm, at the wavelengthof use (e.g., 157 nm, 193 nm, 248 nm, 365 nm).

When being used as a bottom anti-reflective coating, it is preferredthat the compositions be applied in quantities such that the thicknessof the layer 14 after curing or crosslinking will be within about 20% ofthe first maximum thickness of the composition. The first maximumthickness of a composition is defined as:

${{{First}\mspace{14mu}{Maximum}\mspace{14mu}{Thickness}} = \frac{\lambda}{2n}},$where λ is the wavelength of use, and n is the real component of therefractive index of the composition. Even more preferably, the thicknessof the crosslinked layer 14 is within about 15%, even more preferablywithin about 10%, and even more preferably within about 5% of the firstmaximum thickness of the composition. The use of the photosensitivecomposition at these thicknesses results in improved properties,including the ability to print structures with critical dimensioncontrol and to provide adequate coverage for reflection control overtopography.

Compositions for Use in the Invention Method

As mentioned above, the composition used for the present process shouldbe thermally crosslinkable and photosensitive (i.e., photochemicallydecrosslinkable). The preferred compositions will comprise acrosslinkable polymer, oligomer, and/or monomer dissolved or dispersedin a solvent system along with a photoacid generator (PAG) a crosslinker(referred to interchangeably with crosslinking agent).

Suitable polymers include those selected from the group consisting ofaliphatic polymers, acrylates, methacrylates, polyesters,polycarbonates, novolaks, polyamic acids, polysulfonyl esters,polycarbonate-sulfones (i.e., polymers which include recurring monomershaving both an —SO₂ group and a —CO₃ group), and mixtures thereof.Suitable solvent systems, crosslinkers, PAGs, and ingredient quantitiesinclude any of those discussed below.

One suitable composition is disclosed in U.S. patent application Ser.No. 11/683,309, incorporated by reference here. This type of compositioncomprises a compound selected from the group consisting of polymers,oligomers, and mixtures thereof dissolved or dispersed in a solventsystem. The compound is preferably present in the composition at a levelof from about 0.5-10% by weight, preferably from about 0.5-5% by weight,and more preferably from about 1-4% by weight, based upon the totalweight of all ingredients in the composition taken as 100% by weight.

If the compound is a polymer, it is preferred that the average molecularweight be from about 1,000-100,000 Daltons, and more preferably fromabout 1,000-25,000 Daltons. Preferred polymers include those selectedfrom the group consisting of aliphatic polymers, acrylates,methacrylates, polyesters, polycarbonates, novolaks, polyamic acids, andmixtures thereof.

If the compound is an oligomer, it is preferred that the molecularweight be from about 500-3,000 Daltons, and more preferably from about500-1,500 Daltons. Preferred oligomers include substituted andunsubstituted acrylates, methacrylates, novolaks, isocyanurates,glycidyl ethers, and mixtures thereof.

Regardless of whether the compound is an oligomer or polymer, andregardless of the structure of the polymer backbone or oligomer core, itis preferred that the compound comprise an acid functional group. Theacid group is preferably present in the compound at a level of at leastabout 5% by weight, preferably from about 5-90% by weight, and even morepreferably from about 5-50% by weight, based upon the total weight ofthe compound taken as 100% by weight. Preferred acid groups are groupsother than phenolics, such as carboxylic acids (—COOH).

Unlike prior art compositions, the acid group is preferably notprotected by a protective group. That is, at least about 95%, preferablyat least about 98%, and preferably about 100% of the acid groups arefree of protective groups. A protective group is a group that preventsthe acid from being reactive.

Because protective groups are not necessary with the present invention,it is also preferred that the compound is not acid-sensitive. Anacid-sensitive polymer or oligomer is one that contains protectivegroups that are removed, decomposed, or otherwise converted in thepresence of an acid.

In another embodiment, a combination of protected acid groups andunprotected acid groups could be utilized. In these embodiments, themolar ratio of protected acid groups to unprotected acid groups is fromabout 1:3 to about 3:1, and more preferably from about 1:2 to about 1:1.

In embodiments where the composition is being used as a bottomanti-reflective coating, the composition comprises a chromophore (lightattenuating compound or moiety). The chromophore can be bonded with thecompound (either to a functional group on the compound or directly tothe polymer backbone or oligomer core), or the chromophore can simply bephysically mixed in the composition. The chromophore should be presentin the composition at a level of from about 5-50% by weight, andpreferably from about 20-40% by weight, based upon the total weight ofthe compound taken as 100% by weight. The chromophore is selected basedupon the wavelength at which the compositions will be processed. Forexample, at wavelengths of 248 nm, preferred chromophores includenaphthalenes (e.g., naphthoic acid methacrylate, 3,7-dihydroxynaphthoicacid), heterocyclic chromophores, carbazoles, anthracenes (e.g.,9-anthracene methyl metacrylate, 9-anthracenecarboxylic acid), andfunctional moieties of the foregoing. At wavelengths of 193 nm,preferred chromophores include substituted and unsubstituted phenyls,heterocyclic chromophores (e.g., furan rings, thiophene rings), andfunctional moieties of the foregoing. The preferred inventivecompositions will also include a crosslinker.

Preferred crosslinkers are vinyl ether crosslinkers. It is preferredthat the vinyl ether crosslinkers be multi-functional, and morepreferably tri- and tetra-functional.

Preferred vinyl ether crosslinkers have the formulaR—(X—O—CH═CH₂)_(n),where R is selected from the group consisting of aryls (preferablyC₆-C₁₂) and alkyls (preferably C₁-C₁₈, and more preferably C₁-C₁₀), eachX is individually selected from the group consisting of: alkyls(preferably C₁-C₁₈, and more preferably C₁-C₁₀); alkoxys (preferablyC₁-C₁₈, and more preferably C₁-C₁₀); carboxys; and combinations of twoor more of the foregoing, and n is 2-6. The most preferred vinyl ethercrosslinkers include those selected from the group consisting ofethylene glycol vinyl ether, trimethylolpropane trivinyl ether,1,4-cyclohexane dimethanol divinyl ether, and mixtures thereof. Anotherpreferred vinyl ether crosslinker has a formula selected from the groupconsisting of

The preferred compositions also contain a catalyst. The preferredcatalyst is an acid generator, and particularly a PAG (both ionic and/ornon-ionic). Any PAG that produces an acid in the presence of light issuitable. Preferred PAGs include onium salts (e.g., triphenyl sulfoniumperfluorosulfonates such as triphenyl sulfonium nonaflate and triphenylsulfonium triflate), oxime-sulfonates (e.g., those sold under the nameCGI® by CIBA), and triazines (e.g., TAZ108® available from Midori KagakuCompany).

The compositions preferably comprise from about 0.1-10% by weight ofcatalyst, and more preferably from about 1-5% by weight of catalyst,based upon the total weight of the polymer and oligomer solids in thecomposition taken as 100% by weight.

Although a thermal acid generator (“TAG”) can be included in theinventive compositions, in a preferred embodiment the composition isessentially free of TAGs. That is, any TAGs are present at very lowlevels of less than about 0.05% by weight, and preferably about 0% byweight, based upon the total weight of the composition taken as 100% byweight.

It will be appreciated that a number of other optional ingredients canbe included in the compositions as well. Typical optional ingredientsinclude surfactants, amine bases, and adhesion promoters.

The compositions of this embodiment are formed by simply dispersing ordissolving the polymers, oligomers, or mixtures thereof in a suitablesolvent system, preferably at ambient conditions and for a sufficientamount of time to form a substantially homogeneous dispersion. The otheringredients (e.g., crosslinker, PAG) are preferably dispersed ordissolved in the solvent system along with the compound.

Preferred solvent systems of this embodiment include a solvent selectedfrom the group consisting of propylene glycol methyl ether acetate(PGMEA), propylene glycol methyl ether (PGME), propylene glycol n-propylether (PnP), ethyl lactate (EL), and mixtures thereof. Preferably, thesolvent system has a boiling point of from about 50-250° C., and morepreferably from about 100-175° C. The solvent system should be utilizedat a level of from about 80-99% by weight, and preferably from about95-99% by weight, based upon the total weight of the composition takenas 100% by weight.

Another composition suitable for use in the present inventive methods isdescribed in U.S. Pat. No. 7,108,958, incorporated by reference herein.The compositions in this embodiment include polymers selected from thegroup consisting of polycarbonates, polysulfonyl esters, andpolycarbonate-sulfones.

In embodiments where the polymer is a polycarbonate, preferredpolycarbonates comprise recurring monomers having the formula

where each of R¹ and R² is individually selected from the groupconsisting of functional moieties of diols, including aliphatic(preferably C₁-C₁₂) diols, aromatic (preferably C₄-C₁₂) diols, andheterocyclic diols). Preferred diols include those selected from thegroup consisting of bisphenols.

In one embodiment, at least one of R¹ and R² is selected from the groupconsisting of functional moieties of the bisphenols (and preferablybisphenol P and/or bisphenol Z). In this embodiment, it is preferredthat the other of R¹ and R² has the formula

where R⁵ is an alkyl group (substituted or unsubstituted, preferablyC₁-C₁₂, and more preferably C₁-C₆), and Ar is an aryl group (substitutedor unsubstituted, preferably at least C₄, more preferably C₄-C₁₂, andeven more preferably C₆-C₁₀).

In another embodiment, when one of R¹ or R² is a moiety of bisphenol A,the other of R¹ and R² is a group other than

Particularly preferred R¹ and R² groups include those having a structureselected from the group consisting of

As used herein, the term “functional moiety” is intended to refer tomoieties of compounds whose respective structures have been altered sothat they may bond with other compounds. For example, the structure

would be considered a functional moiety of bisphenol A, with thehydrogen atoms from each of the —OH groups originally present in thecompound having been removed so that the oxygen atoms can bond withanother compound or moiety.

In embodiments where the polymer is a polysulfonyl ester, the polymerpreferably has the formula

where X¹ is selected from the group consisting of functional moieties ofdiols and dioximes. Preferred diols include aliphatic (preferablyC₁-C₁₂) diols, aromatic (preferably C₄-C₁₂) diols, and heterocyclicdiols. Particularly preferred diols include those selected from thegroup consisting of the bisphenols. Preferred dioximes include aliphatic(preferably C₁-C₁₂) dioximes, aromatic (preferably C₄-C₁₂) dioximes, andheterocyclic dioximes. Particularly preferred dioximes include thosederived from the condensation of an aliphatic diamine (NH₂-carbonchain-NH₂) and substituted or unsubstituted hydroxybenzaldehydes andhydroxyacetyl benzenes. One particularly preferred example is1,4-diacetyl benzene dioxime.

In a preferred embodiments X¹ has the formula —O—Z—O— where Z isselected from the group consisting of substituted and unsubstitutedaryls (preferably at least C₄, more preferably C₄-C₁₂, and even morepreferably C₆-C₁₀), substituted and unsubstituted alkyls (preferablyC₁-C₁₂, and more preferably C₁-C₆), and combinations thereof.Particularly preferred X¹ groups have a structure selected from thegroup consisting of

In formula (II), X² is selected from the group consisting of substitutedand unsubstituted aryls (preferably at least C₄, more preferably C₄-C₁₂,and even more preferably C₆-C₁₀) and substituted and unsubstitutedalkyls (preferably C₁-C₁₂, and more preferably C₁-C₆). Particularlypreferred X² groups include those selected from the group consisting ofphenyls, naphthyls, furyls, thionyls, and anthranyls. It is preferredthat at least one of X¹ and X² includes an aromatic portion or otherlight absorbing group.

In embodiments where the polymer is a polycarbonate sulfone, a preferredstructure for this polymer is

where each of R³ and R⁴ is individually selected from the groupconsisting of substituted and unsubstituted aryls (preferably at leastC₄, more preferably C₄-C₁₂, and even more preferably C₆-C₁₀), and alkyls(preferably C₁-C₁₂, and more preferably C₁-C₆).

At least one of R³ and R⁴ will include an —SO₂ group, and it ispreferred that at least one of R³ and R⁴ includes an aromatic portion orother light absorbing group. Particularly preferred R³ and R⁴ groupsinclude those selected from the group consisting of

Preferably, the polymer has an average molecular weight of from about1,000-100,000 Daltons, more preferably from about 2,000-50,000 Daltons,and even more preferably from about 2,000-20,000 Daltons.

The compositions of this embodiment are formed by simply dispersing ordissolving the polymer(s) in a suitable solvent system, preferably atambient conditions and for a sufficient amount of time to form asubstantially homogeneous dispersion. Preferred compositions comprisefrom about 1-20% by weight polymer, and preferably from about 2-10% byweight polymer, based upon the total weight of the composition taken as100% by weight.

The solvent systems of this embodiment can include any solvent suitablefor use in the microelectronic manufacturing environment. Preferredsolvent systems include a solvent selected from the group consisting ofpropylene glycol monomethyl ether (PGME), propylene glycol monomethylether acetate (PGMEA), ethyl lactate, propylene glycol, n-propyl ether(PnP), cyclohexanone, γ-butyrolactone, and mixtures thereof. The solventshould be present in the composition at a level of from about 80-98% byweight, based upon the total weight of the composition taken as 100% byweight. Preferably, the solvent system has a boiling point of from about100-160° C.

Any additional ingredients are also preferably dispersed in the solventsystem along with the polymer. Examples of suitable additionalingredients include crosslinking agents, catalysts (e.g., PAGs), andsurfactants. Preferred crosslinking agents include aminoplasts (e.g.,POWDERLINK® 1174, Cymel® products), multifunctional epoxy resins (e.g.,MY720, CY179MA, DENACOL), anhydrides, and mixtures thereof. When used,the crosslinking agent is present in the composition at a level of fromabout 10-50% by weight, and preferably from about 15-30% by weight,based upon the total weight of the solids in the composition taken as100% by weight.

Suitable PAGs include both ionic and nonionic PAGs. Examples ofparticularly preferred PAGs include sulfonic acid-type PAGs such asthose sold under the names CGI 261, CGI 1397, and CGI 1311 (CIBASpecialty Chemicals). When used, the PAG should be present in thecomposition at a level of from about 0.05-10% by weight, and preferablyfrom about 2-8% by weight, based upon the total weight of the solids inthe composition taken as 100% by weight.

EXAMPLES

The following examples set forth preferred methods in accordance withthe invention. It is to be understood, however, that these examples areprovided by way of illustration and nothing therein should be taken as alimitation upon the overall scope of the invention.

Example 1 Coating Formulation Made with Non-Light Absorbing Polymer

1. Preparation of Polymer A

In this procedure, 9.00 grams of cyclohexyl acrylate (obtained fromPolysciences, Warrington, Pa.) and 5.01 grams of methacrylic acid(obtained from Aldrich, Milwaukee, Wis.) were added to a 250-ml,two-neck flask equipped with a stir bar, addition funnel with a nitrogeninlet, and condenser with a nitrogen outlet. These reagents weredissolved by adding 50.00 grams of PGME (obtained from Harcross, St.Louis, Mo.) and stirring under a nitrogen atmosphere. In a separatecontainer, 3.00 grams of dicumyl peroxide (obtained from Acros, N.J.)were dissolved in 36.15 grams of PGME, and this solution was transferredto the addition funnel. The flask was immersed in an oil bath and heateduntil the solution started to reflux. Upon reflux, the dicumyl peroxidesolution was added to the monomer solution. The resulting solution wasrefluxed for 24 hours. A very light yellow solution was obtained. Thesolution was cooled to room temperature and transferred to a Nalgenebottle for storage. Molecular weight analysis by gel permeationchromatography using tetrahydrofuran (obtained from Fisher, Fairlawn,N.J.) as the solvent gave a weight-averaged molecular weight of 17,600Daltons. The optical properties of Polymer A are given in Table 1.

TABLE I n at k at n at 193 nm 193 nm 633 nm Thickness (Å) Cauchy ACauchy B 1.6857 0.052 1.5 1410 1.4879 0.00497772. Preparation of Chromophore A

To synthesize Chromophore A, 10.77 grams of tris(2,3-epoxypropyl)isocyanurate (obtained from Aldrich, Milwaukee, Wis.), 19.23 grams of3,7-dihydroxy-2-naphthoic acid (obtained from Aldrich, Milwaukee, Wis.,0.32 gram of tetrabutylphosphonium bromide (obtained from Aldrich,Milwaukee, Wis.), and 70.0 grams of PGME were added to a 250-ml,two-neck flask with stir bar, nitrogen inlet, and condenser. The flaskwas heated to 100° C. in an oil bath for 24 hours with stirring andnitrogen flow. After cooling, the chromophore was precipitated inapproximately 500 ml of water, rinsed once with 100 ml of water, anddried in vacuum oven at 50° C. overnight.

3. Preparation of Vinyl Either Crosslinker

In this procedure, 25.15 g of tetramethylene glycol monovinyl ether,22.91 g triethylamine, and 250 ml THF were added to a 500-ml, 2-neckedflask equipped with a stir bar, addition funnel, condenser, and nitrogeninlet and outlet. The solution was stirred under a low flow of nitrogenand immersed in an ice water bath.

Next, 20.00 g of 1,3,5-benzenetricarbonyl trichloride were dissolved in50 ml THF in a closed Erlenmeyer flask. This solution was transferred tothe addition funnel. The contents of the addition funnel were addeddropwise (over approximately 15 minutes) to the stirring solution oftetramethylene glycol monovinyl ether, triethylamine, and THF. A whiteprecipitate formed upon contact. After addition was completed, the flaskwas removed from the ice water bath and stirred for approximately 2hours at room temperature (about 20° C.). The flask was then immersed inan oil bath, and the slurry was heated and kept at reflux for 3 hours.The flask was removed from the heat and allowed to cool to roomtemperature.

The slurry was then suction filtered to give a yellow solution. Theyellow solution was concentrated using a rotavap to remove the THF. Theyellow oil was dissolved using 100 ml of diethylether. This solution waswashed and extracted twice with 25-ml portions of aqueous, 12.5%tetramethylammonium hydroxide. This was followed with two washing andextraction steps with 50 ml of deionized water. The ether layer wasallowed to settle out and collected. The ether layer was dried by mixingwith 5.0 g of activated basic alumina. The mixture was stirred for 1hour and gravity filtered. The clear yellow liquid was concentrated in arotavap to give a yellow viscous oil.

The vinyl ether crosslinker, 1,3,5-benzenetricarboxylic acid,tris[4-(ethenyloxy)butyl]ester, had the following structure:

4. Preparation of Coating Formulation 1

A bottom anti-reflective coating formulation, Formulation 1, containing1.4364 grams of Polymer A (14% solids in PGME), 0.6033 gram ofChromophore A, 39.5923 grams of PGME, 9.9058 grams of PGMEA (obtainedfrom Harcross, St. Louis, Mo.), 0.4737 gram of vinyl ether crosslinkerprepared above, 0.0232 gram of TPS-OH (obtained from Midori Kagaku,Japan), and 0.0523 gram BBI-106 (obtained from Midori Kagaku, Japan) wasprepared and filtered through a 0.1-micron endpoint filter. The aboveformulation was spin-coated at 1,500 rpm onto a silicon substrate andthen baked at 165° C. The optical constants at 193 nm were measuredusing a variable angle spectroscopic ellipsometer (VASE) and weredetermined to be n=1.557 and k=0.216. The film was rinsed with ethyllactate (“EL,” obtained from Harcross, St. Louis, Mo.) to test thefilm's resistance to the resist solvent, exposed to light from amercury-xenon lamp, post-exposure baked at 130° C. for 90 seconds, andimmersed in developer (MF-319, obtained from Rohm & Haas, MA) for 60seconds. Table II below shows that bottom anti-reflective coatingFormulation 1 had good solvent resistance, and that it can only beremoved by an alkaline developer after exposure.

TABLE II Bottom Anti-Reflective Coating Formulation 1 Film Properties.Thickness after Thickness after Initial Thickness Exposure, PEB %Development Thickness after 20 s % EL and Development change, (Å) (no %change, (Å) EL rinse (Å) strip (Å) exposed exposure) unexposed 758 7731.6 0 100 770 0.39

Example 2 Coating Formulation Made with Light-Absorbing Polymer

1. Preparation of Polymer B

In this procedure, 21.29 grains of styrene (obtained from Aldrich, St.Louis, Mo.), 26.17 grams of t-butyl methacrylate (obtained from Aldrich,Milwaukee, Wis.), 25.22 grams of methacrylic acid, and 491.84 grains ofPGME were combined in a 1,000 ml, three-neck flask equipped with amagnetic stir bar, thermometer, addition funnel with nitrogen inlet, andcondenser. A solution of 1.81 grams of2,2′-azobis(2-methylpropionitrile) (“AIBN,” obtained from Aldrich,Milwaukee, W), and 164.32 grams of PGME were added to the additionfunnel. The flask was heated to 100° C. in an oil bath with stirring andnitrogen flow. After the contents of the flask reached 100° C., the AIBNsolution was added to the reaction. Upon complete addition, the reactionwas kept at 100° C. for 24 hours. After cooling, the polymer wasprecipitated in approximately 4 liters of hexanes, rinsed two times with200 ml of hexanes, and dried in a vacuum oven at 50° C. overnight.

2. Preparation of Coating Formulation 2

To make the coating Formulation 2, 0.1006 gram of Polymer B, 0.302 gramof Chromophore A, 35.5438 grams of PGME, 8.8929 grains of PGMEA, 0.4737grain of vinyl ether crosslinker prepared above, 0.0309 grain oftriethanolamine quencher (obtained from Aldrich, Milwaukee, Wis.) in 10%PGME solution, and 0.0523 gram BBI-106 were combined and filteredthrough 0.1-micron endpoint filter. The formulation was spin-coated at1,500 rpm onto a silicon substrate and then baked at 160° C. The opticalconstants at 193 nm were measured using a VASE and were determined to ben=1.536 and k=0.272. The film was rinsed with EL to test the film'sresistance to the resist solvent, exposed to light from a mercury-xenonlamp, post-exposure baked at 130° C. for 90 seconds, and immersed indeveloper (MF-319) for 60 seconds. Table III below shows that the bottomanti-reflective coating had good solvent resistance, and that it couldonly be removed by an alkaline developer after exposure.

TABLE III Bottom Anti-reflective Coating Formulation 2 Film Properties.Thickness Thickness After Thickness After Initial After 20-s Exposure,PEB, % Development Thickness EL Rinse % EL and Development Change,(unexposed) % Change, (Å) (Å) Strip (Å) Exposed (Å) Unexposed 592 5991.18 0 100 602 0.50

Example 3 Multi-Patterning Process Using Bottom Anti-Reflective Coating

To make bottom anti-reflective coating Formulation 3, 11.226 grams ofPolymer B, 739.3 grams of PGME, 185.0 grams of PGMEA, 3.306 grams of avinyl ether crosslinker prepared above, 0.859 grains of triethanolaminequencher in 10% PGME solution, and 0.330 grams of a mixture of 50%triphenyl sulfonium perfluoro butanesulfonate and 50%tris-(4-tert-butylphenyl)sulfonium perfluoro butanesulfonate (obtainedfrom Aldrich, Milwaukee, Wis.) were combined and filtered through0.1-micron endpoint filter. To test the multiple patterning process, theformulation was spin-coated at 1500 rpm onto a silicon substrate andthen baked at 160° C. A 1-inch circular mask was placed over the filmand then exposed using a mercury-xenon lamp, post-exposure baked at 130°C. for 90 seconds, immersed in developer (MF-319) for 60 seconds, rinsedwith deionized water, and spin dried. The process left a circle printedon the substrate with a thickness of 54 nm. The exposed areas had nofilm remaining. This wafer was coated once again and processed two moretimes as described above. The resulting wafer had 3 circles printed ondifferent locations on the substrate. This example demonstrates that allfeatures printed before the last exposure remain on the substrate evenafter multiple exposures, bakes, developments, and rinses.

Example 4 Multiple-Patterning Process Using Bottom Anti-ReflectiveCoating

Using Formulation 3 described above, a double-patterning scheme as shownin FIG. 2 was demonstrated. The formulation was spin-coated at 1,500 rpmfor 60 seconds onto a silicon substrate and then baked at 160° C. for 60seconds. A photoresist (AR1682J, obtained from JSR Corp.) wasspin-coated at 3,200 rpm for 60 seconds on top of the bottomanti-reflective coating. The resist and bottom anti-reflective filmswere then baked at 110° C. for 60 seconds. A test (contact) mask wasplaced on top of the wafer, and the films exposed under a mercury-xenonlamp for 5 seconds (at 20 mJ/sec using a 254-nm dose meter). The maskwas then turned approximately 90 degrees from its previous orientation,and the films were exposed for another 5 seconds. The wafer waspost-exposure baked at 110° C. for 60 seconds and then immersed in adeveloper (MF-319) for 60 seconds. The wafer was rinsed with deionizedwater and spin-dried. Overlapping images were observed, showing theimageability of both resist and bottom anti-reflective films.

Example 5 Multiple-Patterning Process Using Bottom Anti-ReflectiveCoating

Using Formulation 3 described above, a double-patterning scheme as shownin FIG. 3 was demonstrated. The formulation was spin-coated at 1,500 rpmfor 60 seconds onto a silicon substrate and then baked at 160° C. for 60seconds. A photoresist (AR1682J) was spin-coated at 3,200 rpm for 60seconds on top of the bottom anti-reflective coating. The resist andbottom anti-reflective coating films were then baked at 110° C. for 60seconds. A test (contact) mask was placed on top of the wafer, and thefilms exposed under a mercury-xenon lamp for 5 seconds (at 20 mJ/secusing a 254 nm dose meter). The wafer was post-expose baked at 110° C.for 60 seconds then immersed in developer (PD523, obtained from MosesLake Industries) for 60 seconds. The wafer was rinsed with deionizedwater and spin-dried. A second coat of photoresist was applied (AR1682J,3200 rpm, 60 sec.). The resist and bottom anti-reflective films werethen baked again at 110° C. for 60 seconds. The mask was then turnedapproximately 90 degrees from its previous orientation, and then thefilms were exposed for another 5 seconds. The wafer was post-exposebaked at 110° C. for 60 seconds and then immersed in developer for 60seconds. The wafer was rinsed with deionized water and spin-dried.Overlapping images were observed, showing the imageability of bothresist and anti-reflective films.

1. A method of forming a microelectronic structure, said methodcomprising: (a) providing a substrate having a surface; (b) applying aphotosensitive composition to form an imaging layer adjacent saidsubstrate surface, said composition comprising a component selected fromthe group consisting of polymers, oligomers, and monomers; (c)crosslinking said component in said imaging layer to yield a crosslinkedimaging layer, said crosslinked imaging layer having a k value of fromabout 0.2 to about 0.5; (d) exposing said crosslinked imaging layer tolight to yield light-exposed portions in said layer; (e) contacting saidlayer with a developer so as to remove said light-exposed portions fromsaid substrate, yielding a patterned imaging layer; and without heatingsaid patterned imaging layer, applying a second photosensitivecomposition to form a second imaging layer on said patterned imaginglayer.
 2. The method of claim 1, wherein no heating occurs during (a),(b), (d), (e), or (f) other than a post-exposure bake after (d).
 3. Themethod of claim 1, said wherein patterned imaging layer and substrateare not etched prior to (f).
 4. The method of claim 1, wherein saidpatterned imaging layer remains intact during (f).
 5. The method ofclaim 1, wherein (c) comprises thermally crosslinking said components.6. The method of claim 1, wherein said second photosensitive compositionis the same as the photosensitive composition of (a).
 7. The method ofclaim 1, wherein said second photosensitive composition comprises acomponent selected from the group consisting of polymers, oligomers, andmonomers, said method further comprising: (g) crosslinking saidcomponent in said second imaging layer; (h) exposing said second imaginglayer to light to yield light-exposed portions in said second imaginglayer; and (i) contacting said second imaging layer with a developer soas to remove said light-exposed portions from said substrate, yielding asecond patterned imaging layer.
 8. The method of claim 7, furthercomprising: (j) optionally repeated (f)-(i) one or more times; and (k)transferring the patterns of the patterned imaging layers to thesubstrate.
 9. The method of claim 8, wherein said (k) comprises etchingsaid patterned imaging layers and substrate.
 10. The method of claim 1,wherein said photosensitive composition further comprises a photoacidgenerator, a crosslinker, and a solvent system, wherein said component,photoacid generator, and crosslinker are dissolved or dispersed in saidsolvent system.
 11. The method of claim 10, wherein said crosslinker isa vinyl ether crosslinker.
 12. A method of forming a microelectronicstructure, said method comprising: (a) providing a substrate having asurface; (b) applying a photosensitive composition to form an imaginglayer adjacent said substrate surface, said composition comprising acomponent selected from the group consisting of polymers, oligomers, andmonomers; (c) crosslinking said component in said imaging layer to yielda crosslinked imaging layer, said crosslinked imaging layer having a kvalue of from about 0.2 to about 0.5; (d) exposing portions of saidcrosslinked imaging layer to light to yield light-exposed portions insaid layer; (e) exposing additional portions of said crosslinked imaginglayer to light to yield further light-exposed portions in said layer;(f) optionally repeating (e); and (g) contacting said layer with adeveloper so as to remove said light-exposed portions from saidsubstrate, yielding a patterned imaging layer.
 13. The method of claim12, further comprising: (h) after (d) and prior to (e), contacting saidlayer with a developer so as to remove said light-exposed portions of(d) from said substrate, yielding a patterned imaging layer.
 14. Themethod of claim 12, wherein no heating occurs during (a), (b), (d), (e),(f), or (g) other than a post-exposure bake after (d) and/or (e). 15.The method of claim 12, wherein said patterned imaging layer andsubstrate are not etched prior to (g).
 16. The method of claim 12,wherein (c) comprises thermally crosslinking said components.
 17. Themethod of claim 12, further comprising transferring the pattern of thepatterned imaging layer to the substrate after (g).
 18. The method ofclaim 17, wherein said transferring comprises etching said patternedimaging layers and substrate.
 19. The method of claim 12, wherein saidphotosensitive composition further comprises a photoacid generator, acrosslinker, and a solvent system, wherein said component, photoacidgenerator, and crosslinker are dissolved or dispersed in said solventsystem.
 20. The method of claim 19, wherein said crosslinker is a vinylether crosslinker.